phengites
From LSJ
phengītes: ae, m., = φεγγίτης>,
I phengite, selenite, or erystallized gypsum, used for window-panes: in Cappadociā repertus est lapis candidus, atque translucens, ex argumento phengites appellatus, Plin. 36, 22, 46, § 163; lapis, Suet. Dom. 14.